There can be a '::' in front of class names to reference from the
top-level namespace.

The method can be followed by parenthesis (not recommended)

CROSSREF_REGEXP

Regular expressions matching text that should potentially have
cross-reference links generated are passed to add_special. Note that these
expressions are meant to pick up text for which cross-references have been
suppressed, since the suppression characters are removed by the code that
is triggered.